When creating a Worker route, either in the web UI or through the API, it’s always done in the context of a zone. You add a route to a zone. Similarly, you list routes for a zone, you get a route on a zone, you update a route on a zone, and you delete a route from a zone.
If you list the workers on an account, each worker includes a list of the routes associated with it (just pattern/script, though - no mention of a zone).
However if you delete a zone, any worker routes set up for it are not deleted - and since the zone no longer exists, it doesn’t seem to then be possible to delete the routes.
Am I missing something in the API? Is there some other way to manage the routes after a zone has been deleted?